Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) were used to study particle size and distribution of sucrose powder. Partial least squares (PLS) regression was used to correlate spectral data with particle size. FTIR-PAS spectra were similar to the spectra obtained using DRIFTS when the sample is mixed with 95% potassium bromide (KBr). Both DRIFTS and FTIR-PAS methods can successfully predict the mean particle size and concentration in binary and quaternary mixtures. R-square values for both DRIFTS and FTIR-PAS are greater than 0.9.